666817920 has 320 divisors, whose sum is σ = 2510362800. Its totient is φ = 168210432.

The previous prime is 666817919. The next prime is 666817927. The reversal of 666817920 is 29718666.

It is a tau number, because it is divible by the number of its divisors (320).

It is a super-2 number, since 2×666817920² = 889292276866252800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666817927) by changing a digit.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 984622 + ... + 985298.

Almost surely, 2^666817920 is an apocalyptic number.

666817920 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 666817920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1255181400).

666817920 is an abundant number, since it is smaller than the sum of its proper divisors (1843544880).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

666817920 is a wasteful number, since it uses less digits than its factorization.

666817920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 727 (or 706 counting only the distinct ones).

The product of its (nonzero) digits is 217728, while the sum is 45.

The square root of 666817920 is about 25822.8178168069. The cubic root of 666817920 is about 873.6465257192.

The spelling of 666817920 in words is "six hundred sixty-six million, eight hundred seventeen thousand, nine hundred twenty".